1. Field of the Invention
This invention relates to an electron-emitting device, an electron source and an image-forming apparatus comprising such an electron source. It also relates to a method of manufacturing such an electron-emitting device, an electron source and an image-forming apparatus.
2. Related Background Art
There have been known two types of electron-emitting device; the thermoelectron emission type and the cold cathode electron emission type. Of these, the cold cathode emission type refers to devices including field emission type (hereinafter referred to as the FE type) devices, metal/insulation layer/metal type (hereinafter referred to as the MIM type) electron-emitting devices and surface conduction electron-emitting devices. Examples of FE type device include those proposed by W. P. Dyke & W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "PHYSICAL Properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 5284 (1976).
Examples of MIM device are disclosed in papers including C. A. Mead, "The tunnel-emission amplifier", J. Appl. Phys., 32, 646 (1961).
Examples of surface conduction electron-emitting device include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10 (1965).
A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface.
While Elinson proposes the use of SnO.sub.2 thin film for a device of this type, the use of Au thin film is proposed in [G. Dittmer: "Thin Solid Films", 9, 317 (1972)] whereas the use of In.sub.2 O.sub.3 /SnO.sub.2 and that of carbon thin film are discussed respectively in [M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)] and [H. Araki et al.: "Vacuum", Vol. 26, No. 1, p. 22 (1983)].
A surface conduction electron-emitting device is typically prepared by arranging a pair of device electrodes on a substrate, bridging the device electrode by means of an electroconductive film made of metal or a metal oxide and then electrically treating the electroconductive film by subjecting it to a current conduction process referred to as "energization forming" in order to produce an electron-emitting region. In the energization forming process, a constant DC voltage or a slowly rising DC voltage that rises typically at a rate of 1 V/min. is applied to the opposite ends of the electroconductive thin film to partly destroy, deform or transform the film and produce an electron-emitting region which is electrically highly resistive. The electron-emitting region is part of the electroconductive film where one or more than one fissures are formed so that electrons may be emitted therefrom.
Since a surface conduction electron-emitting device as described above has a particularly simple structure and can be manufactured in a simple manner, a large number of such devices can advantageously be arranged on a large area without difficulty. As a matter of fact, a number of studies have been made to fully exploit this advantage of surface conduction electron-emitting devices. For example, there have been proposed various types of image forming apparatus including display apparatus.
Examples of the arrangement of a large number of surface conduction electron-emitting devices include electron sources realized by arranging surface conduction electron-emitting devices to form a number of parallel rows of devices and connecting the opposite ends (device electrodes) of the devices of each row to respective wires (also referred to as common wires) (an arrangement often referred to as radder-like arrangement). (See Japanese Patent Application Laid-Open Nos. 1-31332, 1-213749 and 2-257552.) As for display apparatus, there has been proposed a flat panel display apparatus that is similar to a display apparatus utilizing liquid crystal but of an emission type that does not require the use of a back light. Such a display apparatus can be realized by combining an electron source comprising a large number of surface conduction electron-emitting devices and a fluorescent body that emits visible light when irradiated with electron beams by the electron source. (See U.S. Pat. No. 5,066,883.)
However, known electron-emitting devices to be used for electron sources and image-forming apparatus need to be improved in terms of the efficiency of electron emission and other electron-emitting characteristics to provide image-forming apparatus that can stably produce clear and bright images. The efficiency of electron emission is described in terms of the ratio of the electric current running through the surface conduction electron-emitting device (device current If) to the electric current generated by electrons emitted into vacuum from the device (emission current Ie) when a voltage is applied to the paired device electrodes and it is preferable that the device current is held as small as possible whereas the emission current is made as large as possible. If stably controllable electron emitting characteristics and an improved efficiency of electron emission are achieved for a surface conduction electron-emitting device, an image-forming apparatus comprising an image-forming member of a fluorescent body that produces high quality images at a low power consumption rate can be realized by using such devices. Such an image-forming apparatus may be a flat television set and the drive circuit and other components of such an image-forming apparatus may be manufactured at low cost.
Known electron-emitting devices are, however, not satisfactory in terms of stable electron-emitting characteristics and electron-emitting efficiency and hence the stability of operation of an image-forming apparatus comprising such electron-emitting devices is also unsatisfactory.
Therefore, there is a demand for an electron-emitting device that shows excellent electron-emitting characteristics for a prolonged period of time.